Pneumatic control system for aerodynamic surfaces

ABSTRACT

A flight control system for an airfoil comprises a control surface, a chamber connecting the control surface to the airfoil, and a pneumatic mechanism fluidly connected to the chamber. The chamber may be comprised of at least two cells that may be fluidly separated by a membrane. The pneumatic mechanism is configured to provide differential pressure to the cells in order to alternately increase volume/pressure of the cells to cause deflection of the control surface. The cells may have a stretchable outer surface to allow for changes in the length of the outer surface in response to inflation/deflation of the cells. The outer surface of the cells may be substantially continuous with outer mold lines of the airfoil and of the control surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 12/042,443,filed Mar. 5, 2008, issued as U.S. Pat. No. 8,042,772.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

(Not Applicable)

FIELD

The present invention relates generally to aircraft control surfacesand, more particularly, to a flight control system for pneumaticallyactuating a control surface of an aircraft or other vehicle.

BACKGROUND

High altitude and long endurance aircraft such as certain unmanned airvehicles (UAV's) may require wings having a long span and a high aspectratio. Such UAV's may be configured to operate in a loitering capacityat relatively high altitudes (e.g., 50,000 to 80,000 feet) for prolongedperiods of time to provide coverage of a specific geographic area. Thecoverage may include intelligence gathering, surveillance andreconnaissance operations wherein information may be gathered by the UAVand transmitted to ground units or other air units.

Although UAV's may be ground-launched from a runway in the conventionalmanner for aircraft, in some applications it is desirable to deploy theUAV as a payload of another vehicle. For example, in applicationswherein the geographic area where surveillance is desired is far awaysuch as overseas, it may be desirable to transport the UAV to a chosenlocation such as via an intercontinental ballistic missile (ICBM) orwithin the payload bay of a larger aircraft such as a long-range bomberor airlifter. Upon reaching the desired location, the UAV may beseparated from the ICBM or air-dropped from the larger aircraft.

In order to permit packaging of the UAV into the small confines of anICBM or into an aircraft for aerial drop, it is necessary to stow therelatively large wings and control surfaces into very small volumes. Onepreferred option for stowing the wings is to configure the wings to becompactable in the payload bay of the missile or larger aircraft suchthat the wings can be inflated following deployment of the UAV.Furthermore, for aircraft designed to operate in hostile airspace, it isalso desirable to minimize the radar visibility or signature of theloitering UAV to increase its survivability. One method for minimizingradar visibility in aircraft is to use materials that are non-reflectiveto radar such as certain non-metallic materials.

Fortunately, most materials used in the construction of inflatable wingsare non-metallic such that the wings themselves are typically radartransparent. However, while the wing structure may be radar transparent,current mechanisms for actuating the control surfaces of the wings suchas ailerons, flaps and leading edge devices require the use ofmechanisms and/or materials that may not be radar transparent. Even ifsuch current mechanisms are inherently radar transparent, they maypossess certain drawbacks and deficiencies that detract from theiroverall utility.

For example, one option for minimizing the radar transparency of controlsurfaces is to eliminate the control surfaces altogether. However,because most aircraft require some type of mechanism for controlling theaircraft flight attitude, it is necessary to relocate the controlmechanism to the propulsion system. Unfortunately, arranging thepropulsion system to provide the aircraft with directional flightcontrol capability may necessitate the use of independently controllablethrottles on at least two separate propulsion units.

Furthermore, providing directional control via the propulsion unitsrequires the use of thrust-vectoring devices integrated within thepropulsion units. Although such propulsion systems are available, theyare also necessarily complex, costly, bulky and heavy. A furtherdrawback associated with the use of the propulsion system as the sourceof directional control is that a loss of power in the propulsion systemnot only results in a loss of propulsive force to the aircraft, but alsoa loss in directional control of the aircraft.

Another option for actuating the control surfaces of an aircraft isthrough the use of electromechanical actuators. Such electromechanicalactuators may be mounted in the wing and may be used to manipulate theflight control surfaces (e.g., ailerons, flaps, etc.) in order tocontrol flight direction and attitude. Unfortunately, because mostelectromechanical actuators are constructed of metallic materials, theytypically exhibit high radar reflectivity. Furthermore, manyelectromechanical actuators include electric motors constructed withferrous materials that also exhibit high radar reflectivity. Evenfurther, power is typically provided to the electric motors through theuse of metallic wiring extending through the aircraft and which act asradar antennae when extending through the wings to the electromechanicalactuators.

A further option for actuating the control surfaces of an aircraftinclude the use of piezoelectrics wherein piezoelectric strips aremounted on and/or under the surfaces of the inflatable wings such asnear the trailing edge. A positive or negative voltage is applied to thepiezoelectric strips to cause the strips to expand or contract andtherefore curve upwardly or downwardly. If the strips are mounted on thewing near the trailing edge, the trailing edge is also caused to curveupwardly or downwardly such that the portion of the trailing edge mayfunction as an aileron or flap. Unfortunately, the piezoelectric stripsoperate via dielectric (i.e., voltage) potential which is the verymechanism by which radar sees a surface and therefore rendering suchpiezoelectric strips unsuitable for use in aircraft requiring radartransparency.

An even further option for actuating control surfaces includes wingwarping techniques such as that which was employed by the WrightBrothers for roll control of their experimental aircraft. Wing warpingis facilitated through the use of a system of cables and pulleys fortwisting the trailing edges of the wings. Unfortunately, the use of wingwarping on certain aircraft may result in certain disadvantages such asaerodynamic drag due to exposed cables. Although modern cables areavailable in radar transparent materials, the exposed cables impose asignificant aerodynamic drag penalty which increases with the increasingspeed of the aircraft.

As can be seen, there exists a need in the art for a system and methodfor actuating a control surface that has low radar visibility or isradar transparent. Furthermore, there exists a need in the art for asystem and method for actuating a control surface that is predictableand which does not impose excessive aerodynamic drag penalties on theaircraft. Additionally, there exists a need in the art for a system andmethod for actuating a control surface that is of simple construction,light weight and low cost.

BRIEF SUMMARY

The present invention specifically addresses the above-described needsassociated with control systems having low radar visibility by providinga pneumatic control system for a flight control surface that may bemounted on an airfoil such as on an aircraft wing. The technical effectsof the invention include the low radar visibility of the control systemas an improvement over conventional control surface actuation systemswhich are radar visible and/or which are complex and/or which imposeweight or aerodynamic drag penalties on the aircraft.

The flight control system comprises at least one control surface, achamber connecting the control surface to the airfoil, and a pneumaticmechanism for actuating the chamber. The chamber may be formed with oneand, more preferably, a pair of cells that may be separated from oneanother by at least one membrane that is preferably of constant length.

The pneumatic mechanism is fluidly connected to the cells and isconfigured to effectuate or cause a volume change or differential in thecells in order to actuate or move the control surface. Such volumedifferential occurs as a result of the pressurization/inflation of onecell and/or the de-pressurization/deflation of the remaining cell inorder to deflect the control surface upwardly or downwardly. In thismanner, the pneumatic mechanism is configured to dynamically inflateand/or deflate the pair of cells in order to differentially add andsubtract length from stretchable outer surfaces that define the cells.

The membrane may preferably comprise a unitary structure or layer.However, the membrane may be provided in alternative constructions,shapes, sizes and configurations including, but not limited to,multi-layer arrangements or arrangements comprising multiple components.In addition, the chamber may be configured such that the cells aredisposed in either contacting or non-contacting relation to one another.The membrane may be configured to remain at a substantially constantlength between the airfoil (e.g., wing) and the control surface and ispreferably configured to be non-stretchable. The membrane may beflexible in order to facilitate upward and downward actuation of thecontrol surface during inflation and deflation of the cells.

The cells may be stacked atop one another although other arrangementsare contemplated. The outer surfaces of the cells may be arranged so asto provide a continuation of the curvature of mold lines that define theairfoil and, in this regard, the outer surfaces of the cells arepreferably substantially flush with the mold lines and with the controlsurface. The outer surfaces of the cells are preferably fabricated ofstretchable material in order to facilitate inflation and deflation ofthe cells while minimizing pillowing.

The control surface may be configured as a trailing edge device or aleading edge device and may further be provided in a fixed or rigidconfiguration (e.g., a composite solid), a semi-rigid configuration(e.g., flexible foam) or in an inflatable configuration or anycombination thereof. The control surface and airfoil may be provided ina wide variety of alternative configurations including, but not limitedto, a flap or elevon mounted on the trailing edge. The control surfacemay also be configured to be mounted on a leading edge in a variety ofconfigurations including, but not limited to, flaps, spoilers,spliterons, drooping leading edge devices and other configurations. Theairfoil may be provided in a variety of configurations including, butnot limited to, a wing, tail surface or tail section, verticalstabilizer, horizontal stabilizer, stabiliator, elevator, ruddervator,and flaperon.

In one embodiment, the pneumatic mechanism may be configured as a freeair piston having a pair of conduits extending from opposing sides ofthe free air piston to ports on the cells. The conduit material ispreferably radar transparent or a low visibility material such as vinyltubing or other suitable material that facilitates deployment of thewings during inflation. The pneumatic mechanism may include a fillsystem to account for pressure differential that may occur with changesin the ambient pressure as may occur with altitude changes. The fillsystem may comprise a pressurized gas source such as a pressure bottleor an on-board compressor or gas generator.

The free air piston may be comprised of a pneumatic piston slidablycontained within a cylinder or other suitable pressure vessel forcontaining a constant volume of pressurized gas. An actuator may have ashaft which extends into the cylinder to attach to the piston so thatthe actuator can translate or move the piston. Conduits extending fromeach side of the cylinder may be fluidly connected to the ports of eachof the cells. Advantageously, the free air piston configuration enablesa higher degree of control surface responsiveness as compared to an opensystem. Due to it closed system configuration, the free air pistonallows for deflection of the control surfaces within a bandwidth anddeflection capability that is similar to conventional aircraft actuationsystems in order to provide the level of responsiveness that is requiredfor directional control of the aircraft.

The flight control system may comprise at least one position sensor tomonitor and/or detect the position of the control surface or piston forfeedback to the actuator. Position sensors may likewise be included withthe pneumatic mechanism to detect the position of the piston tofacilitate regulation of the actuator. The position sensors for thecontrol surfaces may comprise mechanical deflection sensors and/orpressure taps configured to provide pressure measurements inside thepneumatic piston or inside the cells.

The features, functions, and advantages that have been discussed can beachieved independently in various embodiments of the present inventionor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention will become more apparent uponreference to the drawings wherein like numerals refer to like partsthere throughout and in which:

FIG. 1 is an illustration of an aircraft having a pneumatic controlsystem for a flight control surface mounted on a wing;

FIG. 2 is a sectional view taken along lines 2-2 of FIG. 1 andillustrating a chamber connecting the control surface to the wingwherein the chamber includes a pair of cells separated by a membrane;

FIG. 3 is a schematic illustration of a pneumatic mechanism fluidlyconnected to upper and lower cells with the control surface beingoriented in a neutral position;

FIG. 4 is an illustration of the control surface actuated or deflectedinto an upward orientation and further illustrating a piston of thepneumatic mechanism being biased to one side of a cylinder;

FIG. 5 is a sectional view taken along lines 5-5 of FIG. 4 andillustrating upward deflection of the control surface with the lowercell being in an inflated state and/or the upper cell in a deflatedstate;

FIG. 6 is an illustration of the control surface actuated into adownward orientation and further illustrating the piston of thepneumatic mechanism being biased to an opposite side of the cylinderrelative to that which is shown in FIG. 4;

FIG. 7 is a sectional view taken along lines 7-7 of FIG. 6 andillustrating downward deflection of the control surface with the uppercell being in an inflated state and/or the lower cell in a deflatedstate;

FIG. 8A is a sectional view of an embodiment wherein the control surfaceis configured in a drooping leading edge device and which is shown in anon-actuated position;

FIG. 8B is a sectional view of the drooping leading edge device of FIG.8A in an actuated position;

FIG. 9A is a sectional view of a further embodiment of the droopingleading edge device in a non-actuated position;

FIG. 9B is a sectional view of the further embodiment of the droopingleading edge device of FIG. 9A in an actuated position;

FIG. 10 is a schematic illustration of an embodiment of a pneumaticmechanism configured as a dual blow down fill system;

FIG. 11 is a schematic illustration of a further embodiment of thepneumatic mechanism and illustrating the piston positioned on a rightside of the cylinder; and

FIG. 12 is a schematic illustration of the pneumatic mechanism of FIG.11 wherein the piston is positioned on a left side of the cylinder.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes ofillustrating preferred and various embodiments of the invention only andnot for purposes of limiting the same, FIG. 1 is an illustration of anaircraft 12 having one embodiment of a pneumatic control system 10 for aflight control surface 28 mounted on an airfoil 16 such as an aircraftwing 18. In FIG. 1, the control surface 28 is shown configured as anaileron 30 mounted adjacent to a trailing edge 22 of the wing 18.However the control surface 28 and airfoil 16 to which it is attachedmay be provided in a wide variety of alternative configurations.

For example, the control surface 28 may be configured as a flap 34 orelevon mounted on the trailing edge 22. In another embodiment, thecontrol surface 28 may be configured to be mounted on a leading edge 20of the wing 18 in a variety of configurations including, but not limitedto, flaps, spoilers, drooping leading edge devices and variousalternative aerodynamic devices. The airfoil 16 may also be provided ina variety of alternative configurations including, but not limited to, awing, tail surface or tail section, vertical stabilizer, horizontalstabilizer, stabiliator, elevator, ruddervator, flaperon as well asvarious canard configurations and trim devices.

For purposes of the following 18 discussion, the control surface 28 andairfoil 16 to which it is mounted are provided as the wing 18 andaileron 30 shown in FIGS. 1-12 although the various operating principlesof the control system 10 described herein are applicable to any numberof a variety of control surfaces 28 and airfoils 16 in addition to thosementioned above. Furthermore, the control system 10 is not limited toaircraft but may be applicable to any vehicle wherein pneumaticactuation of control surfaces 28 is desired.

Referring to FIG. 1, the aircraft 12 may optionally include a fuselage14 although it is contemplated that the embodiments described herein areapplicable to tailless aircraft or flying wing configurations which lacka fuselage 14 as conventionally known. Furthermore, the embodimentsdescribed herein are applicable to a wide variety of aircraft and arenot limited to inflatable aircraft or unmanned air vehicles (UAV).

In FIG. 1, the flight control system 10 comprises at least one controlsurface 28, a chamber 40 connecting the control surface 28 to the wing18 (i.e., airfoil 16), and a pneumatic mechanism 52 for actuating thechamber 40 via differential pressure pneumatics. The chamber 40 mayextend along at least a portion of the length of the control surface 28.In this regard, the chamber 40 may comprise chamber segments spacedalong the control surface 28 or the chamber 40 may extend along theentire length of the control surface 28.

The shape of the chamber 40 may be dynamically altered by inflatingand/or deflating at least one cell 42 and, more preferably, a pair ofcells 42 in order to differentially add and subtract length fromstretchable outer surfaces 46 that define the cells 42. In oneembodiment, the cells 42 may be separated from one another by a membrane44 that is preferably of constant length.

The pneumatic mechanism 52 is fluidly connected to the cells 42 and isconfigured to effectuate or cause a pressure differential or volumechange in the cells 42 in order to actuate or move the control surface28. Such differential pressure or volume change occurs during inflationof one cell 42 and/or deflation of the remaining cell 42 in order tocause the control surface 28 to deflect upwardly or downwardly,depending upon which cell 42 is inflated, as will be described ingreater detail below.

Referring to FIG. 2, the membrane 44 can be seen as extending from awall 26 of the wing 18 and back toward the control surface 28. The cells42 that make up the chamber 40 may be fluidly separated from one anotherby the membrane 44. Although the membrane 44 is generally shown ascomprising a single unitary structure or layer, it should be noted thatthe membrane 44 may comprise alternative shapes, sizes andconfigurations including, but not limited to, multi-layer arrangementsor arrangements comprising multiple components. In addition, it iscontemplated that the cells 42 may be configured such that the membrane44 does not function as a common wall for the cells 42. In this regard,the chamber 40 may be configured such that the cells 42 are innon-contacting relation to one another.

Furthermore, although the configuration in FIG. 1 illustrates themembrane 44 as being disposed substantially equidistantly between outersurfaces 46 of the cells 42, the membrane 44 may be attached to the wing18 or the control surface 28 at any position. For example, the membrane44 may be biased toward a lower wing surface and toward a lower side ofthe control surface 28. Regardless of its orientation, the membrane 44is preferably configured to remain at a substantially constant lengthbetween the airfoil 16 (i.e., wing wall 26) and control surface 28. Inaddition the membrane 44 is preferably configured to be non-stretchableto facilitate the constant length characteristic. Furthermore, themembrane 44 is preferably configured to be flexible in order tofacilitate upward and downward actuation of the control surface 28during inflation and deflation of the cells 42.

Referring still to FIG. 2, the cells 42 in the illustrated exemplaryembodiment are disposed or stacked atop one another although otherarrangements are contemplated. Furthermore, the outer surfaces 46 of thecells 42 in FIG. 2 are illustrated as a continuation of the curvature ofmold lines 24 of the wing 18 (i.e., airfoil 16) in order to maintain theaerodynamics of the wing 18. In this regard, the outer surfaces 46 ofthe cells 42 are preferably substantially flush with the mold lines 24at least at the junction of the outer surfaces 46 with the mold lines24.

Likewise, the outer surfaces 46 of the cells 42 are preferablysubstantially flush with the mold lines 24 of the control surface 28 andpreferably at a location of the junction therebetween in order tomaintain continuity of the mold lines 24 and to preserve theaerodynamics of the wing 18. The outer surface 46 of at least one of thecells 42 is preferably configured to be fabricated of stretchablematerial such as structural fabric in order to facilitate inflation anddeflation of the cell 42 while minimizing pillowing 18 during upward anddownward deflection of the control surface 28. Preferably, the materialfor the outer surfaces 46 of the cells 42 also possesses a suitablestrength-to-weight ratio which may be dictated in part by the inflationpressure of the cells 42. In addition, the material for the outersurfaces 46 of the cells 42 is also preferably radar transparentalthough it is contemplated that non-radar transparent material may beused.

The control surface 28 in FIG. 2 is shown as a trailing edge 22 devicewhich may be provided in a rigid configuration, a semi-rigidconfiguration or in an inflatable configuration or any combinationthereof. For the rigid configuration, the control surface 28 may beconstructed as a rigid solid formed of composite and/or non-metallicmaterials although metallic materials may be employed. For thesemi-rigid configuration, the control surface 28 may be constructed of aflexible or elastic material which may include the use of polymericmaterial such as flexible foam. For the inflatable configuration, thecontrol surface 28 may be configured as a bladder or cell which isattached to the cells 42 of the chamber 40 in the manner shown in FIG.2. Regarding sizes of the control surface relative to the chamber, it iscontemplated that the cells of the chamber may define a width (i.e.,along a chordwise direction of the airfoil) that is greater than a widthof the trailing edge device as is illustrated in the embodiment shown inFIGS. 1-7 although other relative sizes may be provided.

Referring to FIGS. 1-3, the pneumatic mechanism 52 is shown in oneembodiment as a free air piston 54 preferably mounted adjacent to orwithin the fuselage 14 although other locations for mounting thepneumatic mechanism 52 are contemplated. The free air piston 54 has apair of conduits 50 extending from opposing sides and extending throughthe wing 18 to a respective one of the cells 42. The conduits 50 arefluidly connected to the cells 42 at ports 48 in order to providepressurized gas to the cells 42 and/or allow for the release ofpressurized gas. The ports 48 are shown located at a forward end on aside of each of the cells 42 but may be located in any suitable positionand are further not limited to being located on the sides or ends of thecells 42.

The conduit 50 material is preferably, but optionally, a flexible tubingof polymeric material that is also preferably radar transparent or a lowradar visibility material. For example, vinyl tubing may be a suitablematerial from which the conduit 50 may be fabricated although anysuitable material may be used. Preferably the conduit 50 is flexible inorder to facilitate stowage of the wings in the uninflated condition aswell as to facilitate deployment of the wings during inflation thereof.

Referring now to FIG. 3, shown is the pneumatic mechanism 52 in the freeair piston 54 embodiment which advantageously provides an essentiallyclosed air system in order to facilitate relatively rapid deflectionrates of the control surface 28. In this regard, the closed systemprovided by the free air piston 54 configuration enables higherresponsiveness as compared to an open system. The free air piston 54 maybe comprised of a piston slidably contained within a cylinder 60 orother suitable pressure vessel for containing a constant volume ofpressurized gas within the pneumatic mechanism 52.

The piston 56 may be translated by an actuator 68 having a shaft 58extending into the cylinder 60 and attaching to the piston 56 as shownin FIG. 10. Conduits extending from each side of the cylinder 60 may befluidly connected to the ports 48 of each of the cells 42 as shown inFIG. 3. The free air piston 54 may preferably be configured to operatethe control surfaces 28 within a frequency bandwidth and deflectioncapability similar to that which is available in conventional aircraftactuation systems. Depending upon roll, pitch and yaw requirements, suchresponsiveness is desirable for control surfaces 28 such as ailerons 30,rudders, elevators and their related configurations (i.e., ruddervators,elevons, etc.) for directional control of the aircraft 12.

Optionally, the pneumatic mechanism 52 may include a fill system toaccount for pressure differential between the internal pressure in thefree air piston 54 as the ambient pressure changes with altitude or withother atmospheric conditions. The fill system may include a pressurizedgas source 62 such as a pressure bottle 66 similar to that which isshown in FIGS. 10-12 and which is described in detail below.Alternatively, the fill system may comprise a compressor such as anon-board compressor of the aircraft 12. Both sides of the free airpiston 54 or, alternatively, only one side of the free air piston 54 maybe tapped. For example, FIG. 10 illustrates the pressurized gas sourcebeing tapped into two locations of cylinder 60 whereas FIGS. 11 and 12illustrate the pressurized gas source 62 being tapped into only onelocation on the cylinder 60.

FIG. 10 illustrates a dual blow down system comprising a pressurized gassource 62 fluidly connected to a cylinder 60. As can be seen, aregulator 74 may be installed in the conduit 50 connecting thepressurized gas source 62 to the cylinder 60. Each of the pair ofconduits 50 extending between the regulator 74 and the cylinder 60 mayinclude a check valve 76. The check valves 76 prevent gas flow betweeneach side of the cylinder 60. The piston 56 is moved within the cylinder60 by an actuator 68 that may be connected to the piston 56 by the shaft58. The piston 56 is translated in response to control signalsrepresentative of a desired amount of deflection of the control surface28.

In FIG. 10, the cylinder 60 portions A and B are fluidly connected torespective cells 42 (A) and (B) of the control surface 28 such thatmovement of the piston 56 causes differential pressure change in thecells 42 resulting in inflation and deflation of the cells and causingdeflection of the control surface 28. More particularly, in oneembodiment, movement of the piston 56 toward the right inflates cell 42(A) while simultaneously causing cell 42 (B) to deflate such that thecontrol surface 28 is deflected downwardly. Movement of the piston 56toward the left inflates cell 42 (B) while causing cell 42 (A) todeflate such that the control surface 28 is deflected upwardly. In FIG.10, the piston 56 is preferably in the neutral position when thecylinder 60 is pressurized by the pressurized gas source 62.

A single blow down system would be similar to that which is illustratedin FIG. 3 with the addition of the pressurized gas source 62 fluidlyconnected to the cylinder 60 such that each portion of the cylinder 60may receive pressurized gas from the pressurized gas source 62 dependingupon the location of the piston 56. As mentioned above, the piston 56 isdriven and controlled by the actuator 68. A check valve 76 may beincluded to prevent gas flow out of the cylinder 60 toward thepressurized gas source 62.

Solenoids 78 may also be used to prevent airflow toward the pressurizedgas source 62 but may also be configured to regulate air flow in bothdirections through the conduit 50 between the pressurized gas source 62and the cylinder 60. The regulator 74 may also be included to monitorand allow adjustment of the pressure that is provided by the pressurizedgas source 62 which, as indicated above, may be provided as a pressurebottle 66, a compressor and/or a gas generator or any other suitablepressurized gas source.

Referring to FIGS. 11-12, shown is the pneumatic mechanism 52 in analternative embodiment wherein a single conduit 50 connects thepressurized gas source 62 to the cylinder 60. As in the arrangement ofFIG. 10, the piston 56 is driven and controlled by the actuator 68. Thecheck valve 76 may be installed in conduit 50 to prevent gas flow fromthe cylinder 60 toward the pressurized gas source 62. The piston 56divides the cylinder 60 into portions A and B and regulates theapportionment of pressurized gas flow to cells 42 (A) and (B) of thechamber 40 at the control surface 28 similar to that which was describedabove for FIG. 10.

For example, FIG. 11 illustrates positioning of the piston 56 toward theright which causes inflation of cell 42 (A) while simultaneously causingcell 42 (B) to deflate such that the control surface 28 is deflecteddownwardly as shown. FIG. 12 illustrates positioning of the piston 56toward the left in order to inflate cell 42 (B) while causing cell 42(A) to deflate such that the control surface 28 is deflected upwardly.

In an alternative configuration, the pneumatic system may also beconfigured as an open loop system (not shown) wherein a pump or a blowdown gas supply provides pressure differential directly to the cells 42in order to actuate the control surface 28. Such open loop system mayhave a relatively slower response rate than that which is available witha closed loop system. Therefore, open loop systems may be more suitablefor actuation of control surfaces 28 that are designed to change thecamber, profile or other geometry of the airfoil 16 such as the wing 18.For example, flaps 34 or drooping leading edges 32 may be effectivelyactuated by an open loop system pneumatic mechanism 52 in order toreduce stall speed or achieve other aerodynamic effects. However, it iscontemplated that any of the open and closed loop systems may be usedfor actuating any control surface 28 configuration described herein oralternative device 28 configurations.

As shown in FIGS. 1-7, the flight control system 10 may further compriseat least one position sensor 72 to monitor and/or detect the position ofthe control surface 28 for feedback to the actuator 68 which preferably,but optionally, operates as a closed loop control system 70 to minimizeerrors. The position sensors 72 may comprise any variety ofconfigurations including mechanical deflection sensors or other devices.For example, position sensors may be provided as pressure tapsconfigured to measure pressure within the cells 42 or within thecylinder 60. Alternatively or in addition, the pressure sensors may bemounted on the surface of the wing 18 to detect changes in pressurealong the surface in response to deflections of the control surfaces 28.

The operation of the control system 10 will now be described withreference to FIGS. 1-7. Referring to FIG. 1, shown is the piston 56 in acenter or neutral position of the cylinder 60 with the control surface28 in FIG. 2 likewise being oriented in a neutral or non-deflectedposition. In this state, the pressure in cells 42 (A and B) as shown inFIG. 3 may be evenly distributed such that neither cell 42 (i.e.,neither A nor B) is inflated to a pressure that is greater than itsstatic pressure level. FIGS. 4 and 5 illustrate the piston 56 as beingbiased toward portion B of the cylinder 60 causing inflation of cell 42(A) and/or deflation of cell 42 (B) of the chamber 40 illustrated inFIG. 5.

The inflation of cell 42 (B) causes an increase in the length of theouter surface 46 of cell 42 (B) which causes the trailing edge 22 todeflect upwardly as shown. The membrane 44 is preferably maintained at aconstant length and may be flexible to facilitate upward deflection ofthe trailing edge 22. Referring to FIGS. 6-7, shown is the piston 56being biased toward portion A of the cylinder 60 causing inflation ofcell 42 (B) and/or deflation of cell 42 (A) of the chamber 40illustrated in FIG. 7. The inflation of cell 42 (A) causes an increasein the length of the outer surface 46 of cell 42 (A) which causes thetrailing edge 22 to deflect downwardly as shown. Similar effects areprovided to other control surface 28 configurations such as leading edgeflaps 34 and drooping leading edges 32.

For example, FIGS. 8A and 8B illustrate a configuration of the controlsurface 28 implemented in a drooping leading edge 32 device. Thedrooping leading edge 32 device may include a fixed portion which may beprovided in a rigid configuration (e.g., a composite solid), asemi-rigid configuration (e.g., flexible foam) or in an inflatableconfiguration or any combination thereof similar to the rigid trailingedge configurations described above. The drooping leading edge 32 deviceis shown as having the fixed portion disposed on the leading edge 20 ofthe airfoil 16. As can be seen in FIGS. 8A and 8B, the membrane 44 maybe formed in a general wedge-shaped configuration wherein the membrane44 may extend generally diagonally upwardly from a lower side of theairfoil 16 and diagonally back downwardly wherein the membrane 44re-attaches to the lower side of the fixed portion. In this regard, themembrane 44 may form the pair of cells 42 (A) and (B) as shown. Inaddition to the fixed portion and the membranes 44 which separates cells42 (A) from (B), the drooping leading edge 32 device may optionallyinclude one or more permeable webs 38 that subdivide cell 42 (A). Eachof the permeable webs 38 is preferably substantially non-stretchable tomaintain the position of the membranes 44 that define cells 42 (A) and(B). Although two of the permeable webs 38 are shown in FIGS. 8A and 8B,any number may be provided.

In FIGS. 8A and 8B, the pneumatic mechanism 52 provides pressuredifferential between cells 42 (A) and (B) in a manner similar to thatwhich was described above with reference to FIGS. 1-7. The droopingleading edge 32 device of FIG. 8A is shown in a static or non-actuatedposition. FIG. 8B illustrates the actuation of the drooping leading edge32 device by inflating cell 42 (A) with cell 42 (B) being simultaneouslydeflated. The permeable webs 38 allow pressurized gas to pass freelythereacross while maintaining their length during the inflation of cell42 (A). The outer surface 46 of cell 42 (A) expands upon inflation whilecell 42 (B) at least partially collapses to cause downward movement ofthe drooping leading edge 32 device. Deflation/inflation of cells 42 A/Bback to their static or neutral pressure causes a return of the leadingedge device to its non-deflected position as is illustrated in FIG. 8A.

FIGS. 9A and 9B illustrate an alternative configuration of a droopingleading edge 32 wherein the membrane 44 extends from an upper side ofthe wing 18 toward a fixed portion of the leading edge 20 of the airfoil16. The rigid portion of the leading edge 20 is similar to thatdescribed above with reference to FIGS. 8A and 8B. Inflation of cell 42(A) cause the outer surface 46 to expand or increase in length withsimultaneous deflation of cell 42 (B) causing the leading edge 20 todrop. As is known in the art, actuation of a drooping leading edge cancause an increase in the airfoil 16 camber which may enhance the liftcapabilities of the airfoil 16 (e.g., wing, elevator).

The above description is given by way of example, and not limitation.Given the above disclosure, one skilled in the art could devisevariations that are within the scope and spirit of the inventiondisclosed herein. Further, the various features of the embodimentsdisclosed herein can be used alone, or in varying combinations with eachother and are not intended to be limited to the specific combinationdescribed herein. Thus, the scope of the claims is not to be limited bythe illustrated embodiments.

What is claimed is:
 1. A method for controlling a control surface of anairfoil comprising: providing a first pressure to a first cell;providing a second pressure to a second cell; changing one of the firstpressure, the second pressure, and the first pressure and the secondpressure such that the second pressure is less than the first pressure;and deflecting the control surface in a direction toward the second cellhaving a pressure lower than the first cell, the first cell and thesecond cell being separated by a substantially nonstretchable membranepositioned between the first cell and the second cell and extending froma wall of a wing to the control surface, and at least one of the firstcell and the second cell connected to the control surface.
 2. The methodof claim 1, wherein the first cell and the second cell are the onlycells positioned between the wall of the wing and the control surface,and further comprising the step of increasing the first pressure to thefirst cell and decreasing the second pressure to the second cell therebydeflecting the control surface toward the second cell and away from thefirst cell.
 3. The method of claim 1 further comprising changing thepressure provided by a pneumatic system in fluid communication with thefirst cell and the second cell.
 4. The method of claim 3 wherein thepneumatic system comprises at least one of a pump or a compressor. 5.The method of claim 3 wherein the pneumatic system comprises a pistonand cylinder.
 6. The method of claim 1, wherein the control surface issubstantially rigid, the first cell and the second cell comprise achamber, and the chamber connects the control surface to the airfoil,and wherein at least one of the first cell and the second cell comprisesa stretchable outer surface, and wherein the membrane is substantiallynon-stretchable.
 7. The method of claim 1 wherein the first cell and thesecond cell each comprise a stretchable outer surface, and wherein aprofile of the first cell and the second cell substantially matches amold line of the airfoil.
 8. The method of claim 1 wherein the controlsurface comprises one of a leading edge and a trailing edge.
 9. Themethod of claim 1 wherein providing the first pressure to the first celland providing the second pressure to the second cell controls apositioning of the control surface configured as one of an aileron,slat, flap, flaperon, elevon, spliteron, and drooping leading edge. 10.The method of claim 1 wherein the first cell and the second cellcomprise a chamber positioned between the control surface and theairfoil.
 11. The method of claim 10 wherein the airfoil comprises one ofa wing, tail surface, vertical stabilizer, rudder, horizontalstabilizer, elevator, ruddervator, stabiliator, and canard.
 12. A methodfor controlling an attitude of a control surface of an aircraftcomprising: providing a first pressure from a free air piston to a firstcell; providing a second pressure to a second cell; changing one of thefirst pressure, the second pressure, and the first pressure and thesecond pressure such that the second pressure is less than the firstpressure; and deflecting the control surface in a direction toward thesecond cell haying a pressure lower than the first cell, the first celland the second cell being separated by a substantially nonstretchablemembrane positioned between the first cell and the second cell andextending from a wall of a wing to the control surface, and at least oneof the first cell and the second cell connected to the control surface.13. The method of claim 12 wherein both the first cell and the secondcell are connected to the control surface, the control surface beingsubstantially rigid, the first cell is positioned above the second cell,the first cell and the second cell are the only cells positioned betweenthe wall of the wing and the control surface, and further comprisinginflating the first cell and deflating the second cell so as to lowerthe control surface.
 14. The method of claim 12 wherein both the firstcell and the second cell are connected to the control surface, thecontrol surface being substantially rigid, the first cell is positionedabove the second cell, and further comprising deflating the first celland inflating the second cell so as to raise the control surface. 15.The method of claim 12 further comprising the step of receiving positioninformation from a position sensor regarding the attitude of the controlsurface.
 16. The method of claim 15 further comprising the step ofchanging the pressure in one of the first cell and the second cell basedon the position information of the control surface.
 17. The method ofclaim 12 further comprising providing fluid through a conduit from apressure source to one of the first cell and the second cell.
 18. Themethod of claim 17 further comprising controlling a fluid flow to one ofthe first cell and the second cell with a solenoid.
 19. The method ofclaim 12 wherein the first cell and the second cell comprise materialsthat are substantially radar transparent.
 20. The method of claim 12further comprising adjusting the first pressure in the first cell andthe second pressure in the second cell as ambient pressure changes.